Means for indicating speed rations and potential rations



July 8, 1941. T. A. KENNY 2,248,504

MEANS FOR INDICATING SPEED RATIOS AND POTENTIAL RATIOS Filed Nov. 23, 1938 :25 1 :Eri

M20 M19 M16 7 (5L4. 8 r I J0 I [NIKE/N71715:.

ATTUFNEK indication.

, the stock as it is Patented July 8, 1941 AND POTENTI Thomas A. Kenny,

AL RATIOS v Mount Lebanon, Pa., assignor of one-half to Raymond A. Siedle, Pittsburgh,

Application November 23,- 1938, Serial No. 241,983

2 Claims.

of means for indicating very slight differences in potential between a plurality of voltage producing sources by distributing the flow of current through the paths of a network circuit including a ratio meter, for such Generally stated, as in the particular use herein illustrated, I utilize two or more elec- This invention consists trlc tachometer generators, so coupled to thesources of differences to be determined, whereby the ratio meter in the circuit network efiects indication of the proportions between generated voltage and such differences, if any. That is to say, by passing the generated potentials through such suitably designed network the current flow through the two coils of the ratio meter is so proportioned that the combined elements with the ratio meter is very much more sensitive than with a directly coupled meter. The important advantage is in effecting a very wide pointer defiection from a comparatively slight change in the ratio of the applied potentials.

W'hilevariously diiierent applications and uses of the invention may be made in various arts and operations, one important field of use is in the art of reducing metal by cold rolling mills, and for illustration such application is presented herein as a good example of several possible applications.

It is a recognized fact in the art of cold rolling strip or sheet material that reduction in gauge is directly proportioned to the increase in speed of discharged from the mill, over the entering spee It may be stated also that somewhat similar methods have been heretofore patented and used for indicating speed ratios in rolling mill practice, but such have not proved satisfactory from the standpoints of accuracy and sensibility when applied to ratios close to unity.

On the contrary my improved method and means eiiecting its success increases the scale spread of the indicating instrument, as a ratio meter. Such wide scale spread, in fact full scale pointer travel, is obtained when used as illustrated on ratios very close to unity, such as 1 1.03; 1:1.05 etc.

Such ratios, closely approximate to unity, may be accomplished and determined over a wide range of speeds without noticeable or material sacrifice in accuracy.

To explain further, the preferred type ratio meter is one using a permanent magnet and moving coils, the current being conducted into and out of the coils by filaments exerting practically no torque. The permanent magnet contributes excellent flux control and inherently makes possible a very sensitive instrument. Since the ratio of currents in the two coils is the only factor influencing their position and hence that of the pointer, the filament torque being negligible, the source voltages may vary Widely, so long as they do so proportionally, without change in the pointer deflection. It should be understood however that the network connection as described ably coupled to rolls may also be used to advantage with a dynamometer type ratio meter. I I 3 In steel' mill application my invention presents one of its most useful applications in'continuously indicating the percent reduction of cold strip and sheet as it passes through finishing stands, such as temper or skin pass mills, as they are known. v

In the cold reduction of sheet and strip steel, as stated, the reduction obtained is directly proportional to the rate of elongation of the metal, i. e. the diflerential between delivery and entry speeds.

Likewise it is directly proportional to the increase in speed of the delivered material to that of the entering material.

My invention, in common with some of those prior to it, prefers to use electric generators suitmounted on either side of the mill so arranged as to be rotated at speeds proportional to the entry and delivery speeds of the strip in passing.

Here however the similarity ends, for instead' of connecting the generators directly to a set of instruments, or to a single ratio meter, they are connected into a suitably designed network such that both coils of the ratio meter are at all times by the output of one of the generators only, the output of the other generator simply being in parallel with one of the ratio meter coils and merely'permitting more or less of the energy of its own through Such network makes it meter having identical or very nearly matched coils, arranged to DIOVlde full scale deflection when one of the coils carries say 50% more current than the other, in other words one which provides full scale deflection on a ratio of 1:1.5. and so proportions the current fiow through it such that a 3% or a 5% change voltage outside the network will be reflected int 50? change in as illustrated ment of the invention as applied to a strip mill,

such as a temper pass mill;

Fig. 2 is a schematic wiring diagram of the electrical connections of Fig. l; r

Fig. 3 is a similar diagram embodying a reversing switch, either manual or automatic, to permit reversible operation of the network, in the case of a reversing mill;

Fig. 4 is a view like Fig. 1 showing application to a tandem mill in which reduction of the blank is produced by thedraft of the rolls and by tension applied by the faster rolls with resulting elongation.

Referring now to such application, as in Fig. 1, it shows the working rolls M of any type mill, as for cold rolling of a length of sheet or strip metal 2. The entry and delivery reels 3 and 5 respectively feed and absorb the strip 2..

The strip in its passage is in operative frictional contact with standard resiliently mounted deflector, tension or "billy" rolls 5 and 5, subject to rotation by the frictional passage of the strip over them. Geared or otherwise coupled to rolls 5 and 6 by suitable means, are a pair of electric generators 1 and 8, preferably of the magneto type which have straight line speedvoltage characteristic curves. The output from the armatures of such generators is transferred by means of conductors 9 and I0 through network resistors ll and I2 to ratio meter coils l3 and H of magnet l5, for actuation of pointer i6with relation to scale l g It will be understood that Fig. 1 is merely a schematic representation or the several elements and necessary connections.

In passing the strip through the mill M in the direction indicated, entry generator I and delivery generator 1 are wired in series with resistor l2 and ratio meter coil l4 respectively, while each such combination is in parallel with the load of generator 1 consisting of ratio meter coil l3 and resistor l i in series terminating in the lead common to both generators.

The circuit is so designed as. to operate with similar results with either direction of travel of the strip, providing a switch is used, as in Fig. 3, in which case a zero center indicator is preferred.

Assuming that generator 8, when on the entry side of the mill, is operating at a speed prop0rtionally slower than generator I on the delivery side, it can therefore never produce a voltage sufficiently high to cause a current to flow through the load. r

Hence all of the current generated by generator 1 passes through connectors It and coil I4, while part of it passes through the load consisting of coil i3 and resistor II, the rest of it passes through resistor l2 and generator 8 in a reverse direction. Therefore the greater the departure from unityratio the lesser becomes the voltage produced by generator. 8 compared with that of generator I, thus causing a greater proportion or current from generator 1 to be bypassed around coil IS. I

As an example, with properly designed circuit and say a 5% increase in delivery speed over entry speed, generator I' will deliver a total of 3.75 m. a. of which 2.5 m. a. will flow through coil l3, and 1.25 m. a. will pass through generator 8 in the reverse direction. It follows therefore that or course all of it or 3.75 m. a. will pass through coil #Il.

Hence we see that full scale deflection will be obtained in an instrument which inherently will deflect full scale only, when one coil carries 50% more current that the other. Actually the network provides such distribution of current even though the generators themselves are operating at a 5% difference in speed.

In the above example, should the generator speeds in each case ference in the coil currents will be obtained with a 1% or a 10% difference in generator speeds.

. interposition would be possibleto While I mention speed changes of 5% etc.

above, the indicator scale itself may be calibrated percent reduction corredirectly in terms of sponding to the percent speed change.

I show in Fig. 2 a modified or simplified circuit network. including ratio meter coil H in the maincircuit and coil l3 and resistor H in a connecting circuit, as indicated.

However such is not the only alternative combination which may be used. For instance it interchange coil l5 and resistor l2 and then recalculate the circuit constants to provide the desired proportioning of the'current flow through the meter coils, i. e.

one and one half times as much current in one.

coil as in the other.

In Fig. 3, it being assumed that the means, generators I and 8, for generating voltages proportional to he speeds of rotating members with in the circuit of'the ratio meter as in Fig. 1, with suitable current distributing network for reflecting a large diiference in the current flowing through coils I1 and H, the circulation may be reversed by interposition of a double pole double throw switch 24, which transposes coil H and resistor l2 into the network in opposite positions to those shown in Fig. 2, such being required in the case of a reversing mill.

Fig. 4 shows a portion of. a tandem mill in which M18, MIB, and M20 are the driven working rolls in each of three stands.

Tension roll 2! is associated with working rolls MI! but is driven solely by the friction of the sheet upon it. Likewise tension roll 22 is associated with working coils Ml'i.

Consider now tachometer generators I and 1 respectively, disposed on the entry and delivery sides of the stand which houses working rolls M19. Since they are connected by the network herein described to a ratio meter by means of leads 0 and 10 in a manner identical with that shown in Fig. l, the indication obtained will be the percent reduction obtainedacross the entire stand as pointed out above, and this will include be decreased 50%, since their speed-voltage curves are straight lines, the volt:

the reduction caused by the draft of the rolls and the reduction caused by the tension applied by the successive stands.

Now consider in like'manner a ratio meter and network connected by leads 9a and In to tachometer generators 8a, and 1. Any reduction caused by tension applied by the succeeding rolls will be evidenced at the bite of working rolls Ml9, the action beingsimilar to pulling the metal through a die.

Hence if no tension were applied the peripheral speeds of working rolls M l9 and tension roll 22 would be equal. However, any reduction resulting from tension will cause an increase in the peripheral speed of tension roll 22 over that of working rolls M19, the amount of such increase being proportional to the reduction. resulting from tension.

It may be explained further that in the cold reduction of metal there are two places where the radio meter and its associated network are particularly applicable, namely as percentage reduction indicators for each stand of a temper pass or skin pass mill, or across the entire mill, since millsof this type reduce the metal very slightly, 1. e. usually under 6% total.

Also, as percentage reduction indicators to show the reduction being obtained as a result of the application of tension in a tandem mill where there are several stands in a row, and where the greater reduction is obtained due to the draft of the rolls, in addition to such reduction still further reduction is obtained resulting from the fact that considerable tension is applied to the sheet by the succeeding stands, tending to pull the sheet through the slower rolls.

Such reduction occurs at the bite of the slower rolls, hence it becomes possible to obtain a measure proportional to the elongation due to tension by comparing the speed of the working rolls to that of the tension roll on the delivery side of that particular stand. A ratio meter and network so connected therefore serves a dual purpose, in that it indicates the reduction resulting from the application of tension which is usually under ten percent, and also acts as a slip indicator. That is, if the working rolls start to slip,

I in series with a resistor, between the junction or the delivered speed of that stand starts to approach that of the peripheral speed of the work ing rolls. This-is an important function, since excessive slippage invariably results in breakage of the sheet, causing a shutdown of the mill.

While my invention 'is applicable to the importantfield of sheet or strip mill practice, it may The ratio meter coils themselves may be relocated physically in different paths of the network to accomplish the same result. Also the resistors I I or H may be either partially or wholly eliminated, and substituted if. desired, by the normal proportioned resistance of the circuit conductors themselves.

What I claim is: l

1. A network for the purposes described consisting of two voltage sources, one side of each being at a common potential, one source being in series with one ratio meter coil and the other which and the point of common potential is embodied the connection, in series, of the other ratio meter coil and a second resistor.

2. A network for the purposes described consisting of two voltage sources, one side of each being at a common potential, one source being in series with one ratio meter coil and the other in series with a resistor, between the Junction of which and a point of common potential is embodiedthe connection, in series, of the other ratio'meter coil, and a second resistor of the variable type which serves to change the calibration, or scale range, or the ratio meter.

THOMAS A. KENNY. 

